Sodium Sulphate Overview

The hydrate of sodium sulphate is known as Glauber’s Salt after the Dutch/German chemist and apothecary Johann Rudolf Glauber (1604-1670), who discovered it in 1625 in Austrian spring water. He named it sal mirabilis (miraculous salt), because of its medicinal properties: the crystals were used as a general purpose laxative, until more sophisticated alternatives came about in the 1900s.

In the 18th century, Glauber’s salt began to be used as a raw material for the industrial production of soda ash (sodium carbonate), by reaction with potash (potassium carbonate). Demand for soda ash increased and supply of sodium sulphate had to increase in line. Therefore, in the nineteenth century, the Leblanc process, producing synthetic sodium sulphate as a key intermediate, became the principal method of soda ash production.

In 1995, bulk sodium sulphate sold for around $70 per tonne in the US, making it a very cheap material. Probably the largest use for sodium sulphate today is as a filler in powdered home laundry detergents. Total consumption of Na2SO4 in Europe was around 1.6 million tons in 2001, of which 80% was used for detergents. However this use is waning, as domestic consumers switch to liquid detergents which do not include sodium sulphate.

Another major use for Na2SO4, particularly in the US, is in the Kraft process for the manufacture of wood pulp. Organics present in the “black liquor” from this process are burnt to produce heat, needed to drive the reduction of sodium sulphate to sodium sulfide. However this process is being replaced to some extent by newer processes; use of Na2SO4 in the US pulp industry declined from 980 000 tons in 1970 to only 210 000 tons in 1990.

The glass industry also provides another significant application for sodium sulphate, consuming around 30 000 tons in the US in 1990 (4% of total US consumption). It is used as a “fining agent”, to help remove small air bubbles from molten glass. It also fluxes the glass, and prevents scum formation of the glass melt during refining.

Sodium sulphate is important in the manufacture of textiles, particularly in Japan. It helps in “levelling”, reducing negative charges on fibres so that dyes can penetrate evenly. Unlike the alternative sodium chloride, it does not corrode the stainless steel vessels used in dyeing.

Glauber salt, the decahydrate, was formerly used as a laxative. It has also been proposed for heat storage in passive solar heating systems. This takes advantage of the unusual solubility properties (see above), and the high heat of crystallisation (78.2 kJ/mol). Other uses for sodium sulphate include frosting windows, in carpet fresheners, starch manufacture and as an additive to cattle feed. In the laboratory, anhydrous sodium sulphate is widely used as an inert drying agent for organic solutions; Na2SO4 is added to the solution until the crystals no longer clump together.